The instructions stored within DNA are read and processed by a cell in two steps : transcription and translation . TRANSCRIPTION is the process of making an RNA copy of DNA . During transcription , a portion of the cell ' s DNA serves as a template for the creation of the RNA molecule .
RNA , or ribonucleic acid , is chemically similar to DNA , except for three main differences : 1 . RNA contains ribose sugar molecules which have more oxygen atoms than deoxyribose - the molecules found in DNA .
2 . Three of the four nitrogenous bases that make up RNA - adenine ( A ), cytosine ( C ), and guanine ( G ) - are also found in DNA . In RNA , however , a base called uracil ( U ) replaces thymine ( T ) as the complementary nucleotide to adenine .
3 . RNA is made in a single-stranded , non helical form .
DNA
RNA
In some cases , the newly created RNA molecule is itself a final product and serves an important function within the cell . In other cases , the RNA molecule carries messages from DNA to other parts of the cell for processing , most often to manufacture proteins .
Of the different types of RNA , the specific type that carries the information stored in DNA to other areas of the cell is called messenger RNA , or mRNA .
HOW I S D N A T R A N S CR I BE D ?
Transcription occurs in four steps : 1 . Initiation 2 . Strand Elongation 3 . Termination 4 . RNA Processing
STEP 1 Transcription begins when an enzyme called RNA polymerase attaches to the DNA template strand and begins assembling a new chain of nucleotides . In eukaryotes , there are three types of RNA polymerases . RNA polymerase II transcribes the vast majority of eukaryotic genes and produces all the protein-coding mRNAs .
RNA polymerases are large enzymes that work together with specialized cell proteins called transcription factors that help determine which DNA sequences should be transcribed and when . During ‘ initiation ’, RNA polymerases and transcription factors bind to the DNA strand at a promoter region - a specific area that facilitates transcription . This area often includes a specialized nucleotide sequence called the TATA box : TATAAA .